In the joint study on urban seismic disaster of irregular site, the effects of irregular topography site in behavior of ground motions and urban seismic disasters are investigated. The first part of the study the seismic motion observation in China (Tongji University) and Japan(Toyohashi University of Technology) were carried out. From the analysis the results showed the spectral ratios of different earthquake indicate the same tendency for individual observation point regardless of the input earthquake motion, such as the epicenter, incident direction and the magnitude. In order to compare the amplification effects of the observational results and theoretical results, the analysis based on the actual ground conditions has been performed by using 1-dimensional and 2-dimensional model. It was found that the amplification was not influenced very much by the direction and angle of incident wave but by the topographical conditions. From the response analyses of axisymmetric valleys subject
… Moreed to incident waves, it found thata) The corresponding amplification is maximum at the valley center and decreases toward the edges.b) The fundamental resonance frequencies depend only on two parameters, namely, the onedimensional frequency at the valley center and the shape ratio, regardless of the incident wave field and the impedance contrast. The proposed empirical formulas can estimate accurately the fundamental frequencies.c) The fundamental resonance amplitudes at the valley center depend on the shape ratio and the impedance contrast. The proposed empirical formulas can estimate approximately the fundamental resonance amplitudes.In the second part the estimation of earthquake risk in urban areas (Shanghai and Tokyo) are considered. By the using the probabilistic method, the malfunction of the roads and streets during earthquake were influenced by the collapse of houses and building and the destruction of them by fire. From earthquake evacuation risk evaluation, the results showed that the evacuation risks of inhabitants were influenced by population density, the malfunction of the roads and streets and number of refuge islands. And in the study the past histrical earthquakes, subsoil conditions and structural characteristics of residential houses and building , it was found that the earthquake risk in Shanghai were lower than in Tokyo. Less